Communication devices, such as pagers, typically receive and decode radio frequency (RF) signals to recover information contained therein. In many conventional communication devices, a received signal is first converted from the radio frequency at which it is received to baseband, subsequent to which digital data is recovered from the signal. The data is then processed by decoding circuitry, such as a microcomputer or decoder chip, which decodes the included information.
In order to recover the digital data from an incoming signal which includes data symbols, tracking circuitry included within the communication device generally tracks the incoming signal for a predetermined amount of time to acquire peak and valley values, i.e., high and low voltage values, of the signal. During the time in which the signal is tracked, the signal is usually sampled a predetermined number of times per data symbol. Once the incoming signal has stabilized and the peak and valley values have been acquired, the values are stored, and the stored value or values are provided to a threshold detector for computation of voltage thresholds. The threshold detector utilizes the peak and valley values and the thresholds to generate from the incoming signal a stream of digital data for provision to decoding circuitry.
Conventionally, peak and valley values are initialized to predetermined values, such as to values corresponding to ground and the operating voltage. This assures that the tracking circuitry will lock onto the appropriate signal voltages within a given amount of time. However, the initialized peak and valley values often are far removed from actual signal peaks and valleys, requiring a relatively long time for peak and valley acquisition, which can result in missed information.
During peak and valley acquisition, conventional communication receivers also usually modify counters by a single count of the least significant bit when the sampled signal exceeds either a peak or a valley to assure minimum granularity. Modification by a single count of the least significant bit, however, further slows peak and valley acquisition time.
Thus what is needed is a method and apparatus for more rapidly acquiring peak and valley values of a signal received by a communication device.